This invention describes a mechanical to electrical energy conversion device, which uses built-in potential of metal-to-metal junctions to generate varying electrical voltages/currents from vibrations or rotations that have random frequencies, speeds, phases and amplitudes within the broad operating range of the device. Furthermore, the operation principle of the invention enables direct wiring of many similar devices, leading to direct increase of the harvested energy without being affected by the differences in the vibration or rotation characteristics as above.